The invention relates generally to computer input devices and more particularly to a track pad input device that generates and transmits measured (raw) sensor data to a host computer system. Software executing on the host computer system analyzes the raw sensor data to determine the user's action.
A track pad is a touch-sensing planar digitizer input device used instead of, or in conjunction with, a mouse or trackball. During use, an operator places a finger on the track pad and moves the finger along the touch-sensing planar surface. The track pad detects the movement of the finger and in response provides location and/or motion signals to a computer. There are two common types of track pad sensor devices: resistive and capacitive. A resistive track pad sensor is a mechanical sensor that uses two layers of material that are typically separated by air. Pressure from a finger pushes the top layer (generally a thin, clear polyester film) so that it touches the bottom layer (generally glass). The voltage at the contact point is measured and the finger's location and/or motion is computed and transmitted to a host computer system. After the finger is removed, the top layer “bounces back” to its original configuration. A capacitive track or touch pad sensor, in contrast, is a solid-state sensor made using printed circuit board (“PCB”) or flex circuit technology. A finger on, or in close proximity to, a top grid of conductive traces changes the capacitive coupling between adjacent traces or the self-capacitance of each trace. This change in capacitance is measured and the finger's location and/or motion is computed and transmitted to a host computer system.
Referring to FIG. 1, prior art computer system 100 includes track pad device 105 coupled to host computer module 110 via communication path 115. Track pad device 105 comprises sensor 120, data acquisition circuit 125, processor 130, memory 135 and transmit circuit 140. In the case of a capacitive track pad device, as a user's finger(s) is (are) moved over the surface of sensor 120, data acquisition circuit 125 measures changes in the capacitive coupling between adjacent sensor elements (or the self-capacitance of a given sensor element). Processor 130, in conjunction with memory 135, processes the acquired capacitance signals to compute a signal indicating the user's finger position on sensor 120 (e.g., a Δx and Δy signal). In some prior art track pad devices, processor 130 may also determine if multiple fingers are activating sensor 120 and whether certain predetermined finger motions (often referred to as “gestures”) are being made—e.g., “select,” “drag,” “file open” and “file close” operations. At specified intervals (e.g., 50 times per second), the user's finger location and/or motion as determined by processor 130 is transmitted to host computer module 110 via communication path 115. At host computer module 110, receive circuit 145 receives the transmitted track pad signal and passes its information to driver application 150. Driver application 150, in turn, makes the computed sensor information available to other applications such as, for example, window display subsystem application 155. Thus, prior art system 100 utilizes a dedicated processor for measuring and analyzing raw track pad sensor data to generate a signal that indicates a user's action.
One of ordinary skill in the art will recognize that processor 130 may be embodied in a general-purpose processor (e.g., a microprocessor), a microcontroller, or a special purpose or custom designed processor or state machine (e.g., an application specific integrated circuit or a custom designed gate array device). Further, memory 135 is typically used to provide permanent storage for instructions (i.e., firmware) to drive processor 130 and may, optionally, include random access memory and/or register storage. A benefit of the architecture of FIG. 1 is that host computer module 110 does not need to know about or understand the type of data generated by sensor 120. A corollary of this feature is that host computer module 110 does not process track pad sensor data.
It will also be recognized by one of ordinary skill that a drawback to the architecture of FIG. 1 is that the feature set (i.e., what motions are detectable) provided by track pad device 105 is essentially fixed by its dedicated hardware—processor 130 and associated firmware (memory 135). Another drawback to the architecture of FIG. 1 is that each manufactured device 105 includes the cost of processor 130 and associated firmware memory 135. Thus, it would be beneficial to provide a track pad device that overcomes these inherent drawbacks.